Stability of Biochar
Client
NSR (Nordvästra Skånes Renhållnings AB) is a municipal waste management company focused on developing circular and sustainable solutions. One of their initiatives is the production of biochar, where garden waste and other organic materials are converted through pyrolysis – a process that occurs without oxygen.
Biochar is used both as a soil enhancer and to sequester carbon long-term, which helps reduce climate impact. NSR’s biochar project is a key part of their strategy to close the loops and create local solutions for sustainable development.
Background
Biochar is considered a stable material with the potential to store carbon long-term and improve soil properties. The stability of biochar is typically measured using proxy methods, with the ratio of hydrogen to carbon (H/C) and oxygen to carbon (O/C) being common parameters. According to guidelines from the European Biochar Certificates, a H/C value ≤ 0.7 and an O/C value below 0.4 are classified as stable. These values provide information about biochar’s physicochemical properties and can be analyzed using relatively simple methods.
Recently, a method known as the spread index has also been used to measure biochar’s stability optically. Originally derived from geology, where it was used to analyze carbon content in other materials, the spread index measures the aromaticity of polyaromatic structures. This can provide an indication of biochar’s stability, as higher aromaticity (≥ 7 fused benzene rings) suggests higher stability.
Task
The project aims to evaluate and compare different methods for measuring the stability of biochar, with a particular focus on the relationship between aromaticity and stability, through a literature review. The following questions will be addressed:
- How does aromaticity relate to biochar stability?
- How does aromaticity compare to the most common measurement methods (e.g., spread index and H/C and O/C ratios)?
- Are there techniques to directly measure aromaticity, such as with laser or IR spectroscopy?
The goal is to provide a clearer understanding of how well these various methods can estimate and measure biochar stability.
Sustainability Goals Addressed by the Project